Method of determining electric field state of mobile station also in view of electric field state of uplink

ABSTRACT

A method of determining the present electric field state of a mobile station also in view of an uplink electric field state is disclosed. A TPC bit counter is supplied with a received signal processed by a baseband processor, and counts TPC bits contained in one radio frame. An electric field state determining unit measures the electric field strength of the received signal from the base station which has been received by an RF receiver. A received electric field strength measuring unit determines a TPC bit evaluation value from the TPC bit sum calculated by TPC bit counter, determines a received electric field strength evaluation value from the received electric field strength measured by the electric field state determining unit, multiplies the TPC bit evaluation value by the received electric field strength evaluation value to calculates an electric field state evaluation value, and controls an alarm unit, a display unit, and an LED unit based on the calculated electric field state evaluation value for thereby indicating the electric field state.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a mobile station in a mobilecommunications system, and more particularly to a method of determiningthe present electric field state of a mobile station in a mobilecommunications system.

[0003] 2. Description of the Related Art

[0004] Mobile stations in conventional mobile communications systemsmeasure the strength of a received electric field (RSSI (Received SignalStrength Indicator), Ec/No, SIR, etc.) of a downlink from a base stationto a mobile station, and determine the state of the electric field basedon the magnitude of the measured strength of the received electricfield, so that the user can know the present electric field state.

[0005] The above process of determining an electric field state at amobile station in the conventional mobile communications systems takesinto account only the electric field state of a downlink. For thisreason, the determined electric field state may not be in conformitywith an actual electric field state. Stated otherwise, if the electricfield state of a downlink is judged as good, then the conventionalprocess declares an acceptable electric field state even though theelectric field state of an uplink is poor. Consequently, a link may failto be established when the user wants to make a call actually throughthe mobile station, or a link that has been established may bedisconnected during a call.

[0006] Therefore, the conventional process of determining an electricfield state has been problematic in that since it determines an electricfield state by taking into account only the electric field state of adownlink, the determined electric field state may not be he same as anactual electric field state.

SUMMARY OF THE INVENTION

[0007] It is therefore an object of the present invention to provide amethod of determining an electric field state with high accuracy bytaking into account also the electric field state of an uplink.

[0008] To achieve the above object, there is provided in accordance withthe present invention a method of determining the present electric fieldstate of a mobile station in a mobile communications system, comprisingthe steps of counting TPC bits in a plurality of slots in apredetermined period to calculate a TPC bit sum, measuring a receivedelectric field strength of a signal received from a base station,determining a TPC bit evaluation value from the calculated TPC bit sum,determining a received electric field strength evaluation value from themeasured received electric field strength, calculating an electric fieldstate evaluation value from the TPC bit evaluation value and thereceived electric field strength evaluation value, and determining thepresent electric field state of the mobile station based on thecalculated electric field state evaluation value.

[0009] With the above method according to the present invention, theelectric field state of the mobile station is determined also in view ofthe electric field state of the uplink by counting TPC bits. Therefore,the method is capable of producing a highly accurately result inconformity with the actual electric field state.

[0010] The above step of calculating an electric field state evaluationvalue may comprise the step of multiplying the TPC bit evaluation valueby the received electric field strength evaluation value. Thepredetermined period may comprise one radio frame.

[0011] The above and other objects, features, and advantages of thepresent invention will become apparent from the following descriptionwith reference to the accompanying drawings which illustrate an exampleof the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 is a diagram showing a transmission pattern for a DPCH overa downlink;

[0013]FIG. 2 is a block diagram of a mobile station according to anembodiment of the present invention;

[0014]FIG. 3 is a graph illustrating a transmission power controlprocess;

[0015]FIG. 4a is a diagram showing the concept of a conventional processof determining an electric field state; and

[0016]FIG. 4b is a diagram showing the concept of a method ofdetermining an electric field state according to the embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0017] Prior to describing a mobile station according to an embodimentof the present invention, a transmission power control process for anuplink, which serves as a basis for a method of determining an electricfield state according to the embodiment of the present invention, willbe described below.

[0018] In recent years, attention has been drawn to a CDMA (CodeDivision Multiple Access) communications process which is highlyresistant to interference and disturbance as communications process foruse in mobile communications systems. According to the CDMAcommunications process, a transmission side spreads a user signal to betransmitted with a spread code and transmits the spread user signal to areception side, and the reception side despreads the received usersignal using the same spread code as the one used in the transmissionside to obtain the original user signal. The CDMA communications processmakes it possible to use the same frequency band among a plurality ofcommunication events or calls because it allows a plurality oftransmission sides to use respective different spread codes to spreadtheir user signals, respectively, and allows a plurality of users toselect spread codes to be used to despread the received user signals foridentifying the calls. The present invention is concerned with thedetermination of an electric field state based on the uplinktransmission power control technology used in the CDMA communicationsprocess.

[0019] According to the CDMA communication technology, spread codes donot interfere with each other if they are completely orthogonal to eachother. However, since it is difficult to keep all spread codes that areused completely orthogonal to each other, the spread codes in use areactually not completely orthogonal to each other, but have somecorrelative components with respect to each other. These correlativecomponents act to interfere with user signals of their own, resulting ina degradation of the quality of communication events or calls. Sinceinterference components are produced for this reason, such interferencecomponents grow as the number of communication events or callsincreases. If the transmission power from all mobile stations is of aconstant level, then a radio wave from a mobile station near a basestation is so strong that it interferes with a signal from a mobilestation far from the base station, resulting in a so-called near/farproblem. To solve this near/far problem, it is customary to use atransmission power control process for setting the transmission power toa suitable value for an uplink from a mobile station to a base station.

[0020] Specifically, the transmission power control process allows themobile station to increase or reduce the transmission power of an uplinkbased on the value of a TPC (Transmission Power Control) bit in eachslot of a DPCH (Dedicated Physical CHannel) that has been received. Thetransmission power control process is carried out such that the BLER(BLock Error Rate) becomes equal to or smaller than a target value ineach of the base and mobile stations.

[0021]FIG. 1 shows a transmission pattern of a DPCH over a downlink(extracted from the 3GPP (3rd Generation Partnership Project)specifications). As shown in FIG. 1, one radio frame has a frame periodof 10 ms and comprises 15 slots. The 14 slots #1 through #14 except theleading slot #0 have a TPC bit each. The DPCH comprises DPDCHs(Dedicated Physical Data CHannels) and DPCCHs (Dedicated PhysicalControl CHannels), with the TPC bit being included in the DPCCHs. Thebit number NTPC of the TPC bit may be one or two depending on thespecifications. The relationship between the TPC bit pattern and thetransmission power is shown in Table 1 (extracted from the 3GPPspecifications). TABLE 1 TPC bit pattern Transmission power N_(TPC) = 1N_(TPC) = 2 Control 1 11 Transmission power to be increased 0 00Transmission power to be reduced

[0022] As can be seen from Table 1, if the TPC bit is “1” or “₁₁”, thenit indicates an increase in the transmission power from the base stationto the mobile station, and if the TPC bit is “0” or “00”, then itindicates a reduction in the transmission power from the base station tothe mobile station.

[0023] The structure of a mobile station according to an embodiment ofthe present invention is shown in FIG. 2. As shown in FIG. 2, the mobilestation according to the embodiment of the present invention has RFreceiver 10, baseband processor 20, TPC bit counter 30, electric fieldstate determining unit 40, received electric field strength measuringunit 50, alarm unit 60, display unit 70, and LED unit 80.

[0024] RF receiver 10 demodulates a signal from a base station which isreceived by an antenna into a baseband signal. Baseband processor 20processes the baseband signal from RF receiver 10. TPC bit counter 30 issupplied with the received signal processed by baseband processor 20,counts TPC bits contained in one radio frame, and outputs the count as aTPC bit sum. Electric field state determining unit 40 measures theelectric field strength of the signal from the base station which hasbeen received by RF receiver 10.

[0025] Received electric field strength measuring unit 50 determines aTPC bit evaluation value from the TPC bit sum calculated by TPC bitcounter 30, determines a received electric field strength evaluationvalue from the received electric field strength measured by electricfield state determining unit 40, multiplies the TPC bit evaluation valueby the received electric field strength evaluation value to calculatesan electric field state evaluation value, and controls alarm unit 60,display unit 70, and LED unit 80 based on the calculated electric fieldstate evaluation value for thereby indicating the electric field state.

[0026] Examples of the relationship between the TPC bit sum and the TPCbit evaluation value is shown in Table 2 below, and examples of therelationship between the received electric field strength and thereceived electric field strength evaluation value is shown in Table 3below. TABLE 2 TPC bit Uplink electric TPC bit sum evaluation valuefield state 14  0 Poor . . . . . . . . .  0 14 Good

[0027] TABLE 3 Received electric Received electric field strengthDownlink electric field strength evaluation value field state  −25 dBm144 Good . . . . . . . . . −120 dBm  0 Poor

[0028] In Table 2, as the number of TPC bits in one radio frame islarger, the BLER of signals received by the base station is poorer.Therefore, larger TPC bit evaluation values correspond to smaller TPCbit numbers.

[0029] In Table 3, as the received electric field strength has a higherlevel, the received electric field strength evaluation value is larger,indicating a better reception state.

[0030] The relationship between the electric field strength evaluationvalue and the electric field state is shown in Table 4 below. TABLE 4Electric state evaluation value Electric field state 2016 Good . . . . ..   0 Poor

[0031] Because the electric field strength evaluation value iscalculated according to “electric field strength evaluation value=TPCbit evaluation value × received electric field strength evaluationvalue”, the electric field state is judged as better as the electricfield strength evaluation value is higher.

[0032] The standard by which the base station instructs the mobilestation to increase or reduce the transmission power is whether thepresent transmission power level of the mobile station satisfies atarget BLER value preset in the base station or not. A transmissionpower control process is illustrated by way of example in FIG. 3.

[0033] If the mobile station is receiving a TPC bit (“1” or “11”)indicating an increase in the transmission power in successive slots,then the base station is instructing the mobile station to increase thetransmission power level because the present transmission power levelfails to satisfy the target BLER value. Stated otherwise, the presenttransmission power level of the mobile station is low enough to impairthe BLER of the signal received by the base station.

[0034] In a method of determining an electric field state according tothe embodiment of the present invention, the above function is utilizedto determine whether the electric field level of signals transmitted andreceived by the mobile station also in view of the electric field stateof the uplink from the mobile station to the base station.

[0035] In a zone A shown in FIG. 3, the BLER of the received signal islower than a target value. In a zone B, the transmission power controlprocess is carried out in order to equalize the BLER of the receivedsignal to the target value. In a zone C, the BLER of the received signalis equalized to the target value, and the transmission power iscontrolled to keep the target value.

[0036] As can be seen from Tables 2, 3, and 4, even when the receivedelectric field strength evaluation value is a maximum value, if the TPCbit evaluation value is a lowest value, the total electric field stateevaluation value is low, so that the electric field state is judged aspoor. Conversely, even if the TPC bit evaluation value is a highestvalue, when the received electric field strength evaluation value is aminimum value, the total electric field state evaluation value is low,so that the electric field state is judged as poor.

[0037] Examples of operation of the electric field state determiningunit 40 to control alarm unit 60, display unit 70, and LED unit 80 usingelectric field state evaluation values that are obtained are shown inTable 5 below. TABLE 5 Electric field state Number of evaluationElectric Antenna Alarm energized value field state bars threshold LEDs2016 Good (max.) 3 4 . . . 1500 3 . . . 2 1000 2 . . .  500 1 1 . . .Alarm is turned on at 250 or less  0 Poor (min.) Out of 0 range

[0038] With the method of determining an electric field state with themobile station according to the embodiment of the present invention, theelectric field state of the mobile station is determined also in view ofthe electric field state of the uplink by counting TPC bits. Therefore,the method is capable of producing a highly accurately result inconformity with the actual electric field state.

[0039] Heretofore, since an electric field state has been determinedbased on only the strength of the electric field state, the electricfield state is judged based on one parameter, i.e., judged as good ifonly the received electric field strength is of a large value, as shownin FIG. 4a. However, the method of determining an electric field stateaccording to the embodiment of the present invention can judge theelectric field state based on two parameters, i.e., the receivedelectric field strength and the TPC bit sum, as shown in FIG. 4b, andhence can make more accurate decisions than the conventional process.The method of determining an electric field state according to theembodiment of the present invention is therefore capable of the totalelectric field state not only in a reception mode but also in atransmission mode.

[0040] In the above embodiment, the uplink electric field state isdetermined by counting TPC bits contained in one radio frame. However,if the radio wave suffers frequent abrupt changes, then TPC bits may becounted in a plurality of radio frames for determining the uplinkelectric field state more stably.

[0041] In the above embodiment, the electric field state evaluationvalue is calculated by multiplying the TPC bit evaluation value by thereceived electric field strength evaluation value. However, the electricfield state evaluation value may be calculated from the TPC bitevaluation value and the received electric field strength evaluationvalue according to another formula. In the above embodiment, TPC bitscontained in one frame are simply added to calculate a TPC bit sum, anda TPC bit evaluation value is calculated from the TPC bit sum. However,a TPC bit evaluation value may be calculated according to anotherformula, not by simply adding TPC bits.

[0042] While a preferred embodiment of the present invention has beendescribed in specific terms, such description is for illustrativepurposes only, and it is to be understood that changes and variationsmay be made without departing from the spirit or scope of the followingclaims.

What is claimed is:
 1. A method of determining the present electricfield state of a mobile station in a mobile communications system,comprising the steps of: counting TPC bits in a plurality of slots in apredetermined period to calculate a TPC bit sum; measuring a receivedelectric field strength of a signal received from a base station;determining a TPC bit evaluation value from the calculated TPC bit sum;determining a received electric field strength evaluation value from themeasured received electric field strength; calculating an electric fieldstate evaluation value from said TPC bit evaluation value and saidreceived electric field strength evaluation value; and determining thepresent electric field state of the mobile station based on thecalculated electric field state evaluation value.
 2. A method accordingto claim 1, wherein said step of calculating an electric field stateevaluation value comprises the step of multiplying said TPC bitevaluation value by said received electric field strength evaluationvalue.
 3. A method according to claim 1, wherein said predeterminedperiod comprises one radio frame.
 4. A method according to claim 2,wherein said predetermined period comprises one radio frame.
 5. A mobilestation comprising: a TPC bit counter for counting TPC bits in aplurality of slots in a predetermined period to calculate a TPC bit sum;a received electric field strength measuring unit for measuring areceived electric field strength of a signal received from a basestation; and an electric field state determining unit for determining aTPC bit evaluation value from the calculated TPC bit sum, determining areceived electric field strength evaluation value from the receivedelectric field strength measured by said received electric fieldstrength measuring unit, calculating an electric field state evaluationvalue from said TPC bit evaluation value and said received electricfield strength evaluation value, and determining the present electricfield state of the mobile station based on the calculated electric fieldstate evaluation value.
 6. A mobile station according to claim 5,wherein said electric field state determining unit comprises means forcalculating an electric field state evaluation value by multiplying saidTPC bit evaluation value by said received electric field strengthevaluation value.
 7. A mobile station according to claim 5, wherein saidpredetermined period comprises one radio frame.
 8. A mobile stationaccording to claim 6, wherein said predetermined period comprises oneradio frame.